Evaluation of the second hot dry rock geothermal energy reservoir: results of Phase I, Run Segment 5

Abstract

The r e s u l t s o f a long-term (286 day) flow t e s t o f t h e second hot d r y rock reservoir a t t h e Fenton H i l l f i e l d s i t e are presented. This second reservoir was created by f r a ct u r i n g an i n t e r v a l o f g r a n i t i c rock located a t a depth o f 2.93 km (9620 f t) i n t h e same wellbore p a i r used i n the creat i o n of t h e f i r s t , smaller reservoir. The new f r a c t u r e system has a v e r t i c a l extent o f a t l e a s t 320 m (1050 ft), Suggesting t h a t the combined heat-transfer area o f the o l d and new f r a c t u r e systems i s much greater than t h a t o f the o l d system. The v i r g i n rock temperature a t t h e bottom o f the deeper i n t e r v a l was 197OC (386OF) .

A thermo‐hydro‐mechanical coupled model in local thermal non‐equilibrium for fractured HDR reservoir with double porosity

“…If the calibrated material parameters are considered suitable, the fracture spacing can be calculated with equation (72), yielding B = 13 m which matches well the 10 m magnitude proposed in Zyvoloski et al [1981, Figure 3.2]. Furthermore, the solid‐to‐fracture fluid heat transfer coefficient h sf can be estimated to h sf = 0.12 W/m 2 .K.…”

“…(left) Fenton Hill hot dry rock reservoir with k f = 8.010 −15 m 2 and n f = 0.005. Field data pertain to 2703 m (circles), 2673 m (diamonds), 2626 m (crosses), and in the casing 2660 m (squares) [ Zyvoloski et al , 1981]. The optimum specific solid‐to‐fracture fluid heat transfer coefficient κ sf is equal to 33 mW/m 3 .K.…”

“…According to Richards et al [1994], water loss may occur according to three mechanisms: steady state diffusive loss, transient loss into storage and loss due to reservoir growth (propagation of the fracture network). To the exceptions of Zyvoloski et al [1981], Tenma et al [2008], and Ghassemi et al [2008], few studies really address fluid losses into the matrix, permeation being usually imposed by a continuous leak‐off into the formation.…”

Thermal Effects of Reinjection in Geothermal Reservoirs With Major Vertical Fractures

“…and Smith,1%4). Preferential flow paths may be contorted, causing thermal interference between different path segments, which could not be predicted from tracer tests (Zyvoloski, 1981). Due to thermal drawdown over extended injection periods, the flow field may change with time, chiefly from buoyancy and viscosity effects.…”

“…The only type of test which can provide reliable estimates of the heat transfer properties of preferential pathways appears to be a thermal interference test. This has been carried out successfully in small experimental hot dry rock reservoirs (Murphy and Tester, 1979;Zyvoloski, 1981;Dash et al, 1981;Murphy et al, 1981). For conditions of interest in natural hydrothermal systems, however, thermal interference tests cannot be carried out ahead· of a long-term injection program, as required test durations may be many years.…”